p59fyn is a membrane-associated non-receptor protein tyrosine kinase that belongs to the Src-family of kinases. The unique N-terminal domain of p59fyn interacts with the CD3 and eta chains of the TcR. p59fyn can bind other proteins (p82 and p116) through its SH2 and SH3 domains, which may act as substrates or regulators of fyn activity. p59ffyn is highly expressed in brain suggesting that it may have a role in the sensory nervous network and in myelination at early stages of CNS formation.